Mine is absolutely pathetic, but it's mostly because I haven't done any fine tuning since finishing my engine.
On the interstates I do good to get 14-15 mpg if I stay at around 70 mph (which is only 2300 rpms in overdrive). I have headers, HEI, mild cam and an Edelbrock 500 cfm 4 barrel (which hasn't been changed out of the box). I imagine that if I were to tune the carb couple of stages leaner then I'd see an improvement in gas mileage. But I drive the truck so little that I haven't been very enthusiastic about breaking the carb apart and changing the jets and metering rods. I just deal with the dismal gas mileage the 2 or 3 times a month that I drive it.
-ftyler
